Focus is used to indicate which view a user's input will interact with. If the focused view doesn't capture an event, it's propagated up the view tree until it hits the scene's root view. If nothing in the scene captured or blocked the event, the next scene in the scene stack with a focused view receives the event.
Default, Greedy, and Policy
View by default cannot be focused. The Focus Policy property can be used to change if and how a view can be focused. When Request Default Focus is set, the view will be focused when the scene is first shown. When both Request Default Focus and Focus Greedy are set, the view will be focused whenever no other view is focused in the scene.
Focusable views respond to navigation events (which are key events or generated by Focus Navigation nodes) by finding and focusing a view in the specified direction.